FIG. 1 is a schematic view to show a bearing system equipped with journal bearings which use oil as a lubrication fluid. As shown in FIG. 1, the bearing system includes a journal 130 and a stationary part 120. The journal 130, functioning to transmit power, is supported by the journal bearings 110. The journal bearings 110 are secured to the stationary part 120 which is made of a metal. Thus, heat generated in the journal bearings 110 is transmitted through the journal bearings 110 to the stationary part 120. When the temperature of lubricating oil rises in the journal bearings 110, thus the viscosity of the oil is reduced, and thereby a breakage of a lubrication film may be caused. Accordingly, in order to prevent the breakage of the oil film, heat conductivity of each journal bearing 110 is one of very important characteristics of a bearing.
Further, when the journal 130 starts or stops rotating, there is no enough pressure generated to support the journal 130 by a lubrication oil film, so that boundary lubrication condition occurs, that is, a part of each journal bearing 110 is in direct contact with the journal 130. When the journal bearings 110 are broken or damaged due to the contact between the journal 130 and the journal bearings 110 under the boundary lubrication condition, the friction coefficient and relative hardness between the journal 130 and the journal bearings 110 are recognized as important factors for bearing characteristics. When the journal 130 is driven under the boundary lubrication condition, a surface of the journal 130 may be damaged due to the contact between the journal 130 and the journal bearings 110. Further, viscosity of the lubrication oil is reduced by heat generated due to the contact between the journal 130 and each journal bearing 110, and a load bearing capacity of each journal bearing 110 is reduced, so that each journal bearing 110 may be undesirably adhered to the journal 130, thus causing seizure of each journal bearing 110 to the journal 130. Meanwhile, when an excessive load acts on each journal bearing 110 or viscosity of the lubrication oil is reduced, the oil film becomes thin, so that the above problems may occur.
Thus, in order to protect the rotating journal 130 and reduce generation of heat due to the friction between the journal 130 and each journal bearing 110, each journal bearing 110 must be made of a material which has lower hardness compared to the journal 130, and a lower friction coefficient and a high thermal conductivity coefficient.
Now, a white metal has been widely used as a material of a liner of the journal bearing. The liner is laminated to an inner surface of a metal housing having a circular cross-section. The white metal is an alloy including tin, lead, antimony, and copper, and meets the above-mentioned requirements of the journal bearing. However, the white metal has problems as follows. That is, since the white metal is a kind of metal, the white metal may be undesirably adhered to the journal made of a metal, due to melting caused when the white metal of the journal bearing is in direct contact with the journal and thereby temperature rises. Meanwhile, when the journal is made of a non-metal material, such as a composite, the journal may be broken or damaged due to relatively higher hardness of the white metal when there is friction between the journal bearing and the journal.
The journal bearing may be integrally manufactured using a glass fiber reinforced phenol composite which has a lower friction coefficient and relatively lower hardness. However, such a journal bearing is made of only the composite, so that the thickness of the journal bearing is increased. Due to the increased thickness, a physical property is deteriorated during the curing of the composite, and oil is absorbed in the composite during the operation of the journal bearing, so that dimensional precision is reduced, thus causing the journal bearing to be unstably driven. Thereby, the journal bearing may be broken or damaged. Further, since the composite absorbs oil during the operation of the journal bearing, the lubrication film is destroyed during the operation of the journal bearing or the oil film becomes thin, so that the journal bearing may be severely damaged.